The W.D. Vindicated.
If you've noticed an error in this article please click here to report it so we can fix it.
The Suitability of the Subsidy Models Proved in Actual Service.
By the Man Who Stayed at Home.
rf his contributor emphasizes our own confirmed that, as a Government machine, the British subsidy war we hops to see more definite distinction between opinion, to which we have always given expression, model is a very difficult one to beat. After the subvention inodels' and subsidized types.—ED.] „.
I have, since the commencement of the war, derived considerable pleasure fromthe perusal of ;he " De: Spatches from the Front "which have appeared weekly in your journal. The matter therein containecahas always been interesting, not only to the technical man, but also, I am sure, to the lay reader. Personally, I have on many occasions, when satiated with the reports and counter reports of the situation as found in the daily papers, turned to the notes from our various correspondents with Considerable .relief. ,They vary in the nature of their contents week by week. The interest up to now has been principally, Of course, in hearing how my many friends are going On in the transport columns at the Front.
Your correspondents deal from time to time in a very .bright and lucid manner with the shortcomings of the various types of lorry which they are using over there. In reading their notes, and particularly those in your .last issue wherein attention is drawn to what, in your correspondent's opinion, are desirable features in a .motor lorry meant for use as a war-transport vehicle, I could not help but notice how closely his specifica-tion compares with the current one issued by our War Office, and to which subsidy models are, of course, still -being built.
As I myself have had an experience of this model almost unique in its thoroughness, my interest in this -matter is of more than ordinary intensity. Further., as have all along been of opinion that the Mechanical Transport Committee of the War Department has shown a thorough knowledge of its own requirements iP the drawing up of the specification, I was considerably gratified to read this strikingly-corrobora.tive evidence, from such a source.
Taking the points raised by him seriatim, he commences by noting that the lighter lorries are most suitable for delivering food and ammunition, and he points out that this duty "demands a small but powerful and heavily-constructed lorry, though not necessarily what is termed a heavy one "—" the ideal lorry for food supply appears to be the 30-cwt. type, though if made for the job it would be better to make it considerably stronger, and fit it with a more powerful engine than is usually necessitated for Prdinary service." I think this aptly summarizes the War Office specification of lorries type B to carry a useful load of 30 cwt. The objection to this type from a nommercial point Of view has always been that it was heavier than the normal 30-cwt. loitY, and, further, there is no doubt that the size of engine specified by the W.D., a. 4 in. minimum, is considerably larger than is usually found on a lorry for carrying such a load.
Your correspondent next deals with the question of the gearbox, and suggests that a four-speed box is desirable, including a very low gear for use in extra arduous work ; in his opinion also with the third gear in use, and engine running at normal speed, the speed of the lorry should be 12 miles per hour. As a matter of fact all these requirements are insisted on in the Government specification. A four-speed box is a necessity, and from a calculation of speeds derived from the gear ratios which the War Office stipulate, I find that, with engine running at 1000 revolutions--Per minute, and the third speed engaged, with a heavy lorry 10 miles per hour will be obtained, and on the third speed of the lighter or 30-cwt. type, 11 m.p.h.
I consider this to be sufficiently near to your correspondent's reqiiiroments. Referring to the engine, he suggests one of 35 hp. I presume he is now dealing with the heavier type of lotry, and here again I might point out that the War Office, specify as a minimum a in. engine, which Of course, easily develop that power.'. That the cylinders should be east in pairs has also been stipulated. Lubrication of an engine which is required to work in such circumstances as must occur in war time is naturally one of the most important points. Your correspondent rightly suggests that the capacity for oil should be great, so that it may be possible to run for long periods without the necessity for replenishing. Here, again, I may say the responsible officials at Whitehall have evidently appreciated this point. This specification calls for a reservoir to carry sufficient oil to last a minimum of 200 miles. More is better.
On the question of final drive, I am not in perfect agreenient with your-correspondent. That the chain drive is hardly .suitable for such arduous conditions as are being encountered on the Continent at the present time may be agreed. Quite apart from the objections raised in the article, it seems to me that for such work it is absolutely necessary that the whole of the transmission be enclosed. In the writer's opinion, achain case allowing sufficiently facile access to wheels, brakes, and sprockets, has yet to be designed. We are thus left with the question as to whether worm or bevel should be employed. Hereaal again, I may say, I am speaking from experience of both types, from a practical as well as a theoretical standpoint—I am confident that a double reduction fornsuch;heavy leads as are likely to be placed on the larger-sized subvention model, will be found to be the best type of final drive.
As regards clearance, I am sure that a suitably designed bevel 'andspur drive can be so arranged as to give considerably more room under the axle casing than can be obtained by the use of a worm drive, that is to say, provided the worm be sufficiently strong to stand up to its work and give reliable, continuous, service.
With Degard to silence, your correspondent only repeats arguments which have been already so used time and time again and have been discounted the same number of times with regard -to the final drive of pleasure cars. With careful adjustment and correctly-cut and' hardened gears there is no reason whatever why these should not be made as silent as' the worm and wheel.
Your correspondent's suggestion that a spring drive should be fitted between the engine and back axle is quite an interesting one. There have been several attempts at something of the sort, but for some reason
or other they have, n the main, been abandoned. Personally I am rather of the opinion that the leather joints, at any rate those between the engine and gearbox—now becoming general--.-will to some extent serve the pisepose of a spring coupling. A further point of similarity between the official specification and the suggestions of your correspondent is to be found in that relating to the method of transmitting the drive from the rear axle to the chassis. The' War Office stipulates that a torque and radius rod must be provided and insists that the ,War Office Vindicated—con.
springs must be utilized solely for damping out road • shocks.
In minor details as well as those of more importance
• the same similarity of thought is to be found. Grease cups, for example, are specified iir various places ; the size also is all that can be desired. The large cocks and orifices for rapidly filling and emptying radiators and petrol tanks have not been overlooked. The size of the drain cock for the fuel tank is specified in the original pamphlet, and it was some little time afterwards discovered that the matter of draining the radiator suitably had been overlooked, and this was remedied in a later issue. When perusing these remarks the reader must understand that I am dealing. with the War Office specification and the suitability of the subvention model for war purposes only, and am not discussing the suitability or otherwise of such vehicle for ordinary commercial purposes. Price, weight; engine-power and other factors may not, and in factoften do not, appeal to the buyer who is commercially inclined only. That body of opinion may now be increased. In case the above notes strike the reader as being rather eulogistic and of c` blowing the trumpet" of the War Office, may I add the disclaimer which is usually to be found at the. end of coitespondence addressed to your sister journal "The Motor," to the effect that I have no axe to grind.